Narrated Ali (RA):

"I had the permission of Allah's Messenger (ﷺ) to see him in his house at two times, and whenever I entered to him while he was praying he would clear his throat as a sign to me." [Reported by an-Nasa'i and Ibn Majah].

وَعَنْ عَلَيٍّ ‏- رضى الله عنه ‏- قَالَ : { كَانَ لِي مَعَ رَسُولِ اَللَّهِ ‏- صلى الله عليه وسلم ‏-مَدْخَلَانِ , فَكُنْتُ إِذَا أَتَيْتُهُ وَهُوَ يُصَلِّي تَنَحْنَحَ لِي } رَوَاهُ النَّسَائِيُّ , وَابْنُ مَاجَهْ .‏ [1]‏